Apparatus for adjusting the gram load of head gimbal assemblies

ABSTRACT

The gram load of head gimbal assemblies (HGA) of a head stack assembly (HSA) is adjusted before the HSA is installed in a disk drive. Each HGA includes an elongated flexible member having a bend that is transverse to the longitudinal axis of the HGA. The apparatus includes means for removably mounting the HSA for movement in a plane parallel to the longitudinal axis of the selected HGA to a Gram Load Adjusting (GLA) station, means to restrain movement of the HGA during gram load adjustment, a force-transmitting bar having an elongated bearing edge, means for positioning the bar with the edge parallel to the bend and in force-transmitting contact with the bend area of the flexible element, and means for moving the edge to adjust the gram load to a desired value.

FIELD OF THE INVENTION

This invention relates to the manufacture of Head Stack Assemblies(HSAS) used in rotating magnetic disk drives and in particular to amethod and apparatus for selectively adjusting the gram load of eachHead Gimbal Assembly (HGA) of an HSA to a predetermined value during themanufacturing process and prior to the time that the HSA is installed inthe head positioning system of a disk drive.

DESCRIPTION OF THE PRIOR ART

Typically, a disk drive comprises one or more magnetic disks havingmagnetic surfaces for storing data. The disks are mounted on a spindleand continually rotated at a substantially constant speed. A pluralityof head arm assemblies are arranged together in a stacked assemblyresembling a comb-type structure. The Head Stack Assembly (HSA) isattached to an electromagnetic actuator which is controlled by a headpositioning system. The actuator positions the magnetic heads ortransducers to preselected concentric recording tracks under the controlof an address signal supplied to the actuator from the data processingsystem.

Each head is spaced from the associated disk surface by a film of aircreated by the disk as it is rotated. This type head is referred to inthe art as an air bearing type head. The HGA includes the relativelyrigid section including the nut plate and the flexible Head GimbalAssembly (HGA) section which is rigidly attached by a swaging operationto the nut plate. The HGA includes the magnetic transducer or head whichis mounted to an air bearing slider that is attached to a flexible sheetmetal member or flexure by means of a gimbal type mounting. The head isbiased toward the magnetic surface of the rotating disk by apredetermined bend in the flexible element located adjacent to the nutplate of the HGA.

The transducer is supplied with data signals during the recording modeof the disk drive. During reading of the recorded data, the transducersenses the magnetic transitions recorded on the disk representing thedata. The individually manufactured head arm assemblies that areassociated with each disk surface are assembled into a comb-typestructure with the transducers at the distal ends of the HGAs accuratelyaligned vertically. In a similar fashion, the other ends of the armassemblies must be attached to the actuator so that each arm moves overa corresponding path.

The personal computer and in particular the so called "lap top" modelsof personal computers, have imposed a size parameter on disk files whichis in total opposition to the currently desired capacity requirementsfor data storage. As the need for more storage capacity increases, thereis a need to reduce the size of disk drives. Disk diameter is adominating factor in determining the footprint of the drive. The numberof disks in the stack generally determines the height of the drive. Inthe last few years disk diameters for fixed disk drives used in personalcomputers have decreased from 51/2 inches to 33/4 inches to 11/8 inches.Presently, prototype disk drives employing 1 inch disks are indevelopment. The decrease in size has had little or no impact on storagecapacity, in that the various technologies which directly affectcapacity, such as linear recording density and track density, have beensubstantially improved. Also, configurations now can employ more disksin a given height since a decrease in the spacing between disks has beenmade possible. A major effect of the decrease in size has been theinability to employ past assembly practices in the construction of thesesmaller disk files. For example, as the various components of the HSAbecome smaller, the force which is applied to each magnetic head by theflexible element to bias it towards the disk surface becomes smaller andthe tolerances permitted for this force become very narrow. It is thennecessary to adjust every HGA after assembly into the HSA, not justthose whose initial gram loads were disturbed during assembly into theHSA.

In addition, the individual components on the HGA become more fragileand are easily damaged if extreme care is not exercised during each ofthe assembly operations. A head arm assembly operation generallycomprises joining together a relatively stiff element and a relativelyflexible element by a swaging operation. A head gimbal assembly (HGA)comprising a magnetic transducer and a gimbal type mount is attached tothe distal end of the flexible element, usually by spot welding. Theother end of the flexible element has a nut plate welded to the element.The nut plate includes a cylindrical boss which extends normal to theflat surface of the plate and is designed to mate with an openingdisposed in the end section of the rigid element. The elements arealigned precisely and spot welded to maintain their alignment during thesubsequent swaging operation. The swaging operation involves a series ofsteps in which a cylindrical ball slightly larger than the opening in aboss is forced through the boss thereby cold forming the boss materialto the area of the rigid element surrounding the boss. Three separateoperations are performed, each with a ball having a larger diameter.This swaging operation has become the most critical step in themanufacturing process as the size of the components has decreased andtheir fragility has increased. The biasing force for the magnetictransducer is provided in the flexible element by bending the flexibleelement along a line perpendicular to the lengthwise axis of the arm andsubsequently returning the element to its original position whilesimultaneously stress relieving the bend area by heating it with a laseruntil the desired gram load force is obtained. The required gram load isdetermined by the flying characteristics of the transducer relative tothe magnetic surface.

Assembly operations of the HSA involve providing a guide means, such asa guide hole, in the actuator end of the head arm. Each HGA issequentially placed on a shaft with suitable ring type spacers betweeneach arm. Each arm is affixed to the shaft by ball swaging or adhesive.

The measurement of the gram load on each head of the HSA is currentlyachieved by an operator and a measurement apparatus. The apparatusincludes a horizontal platform that is movable in a straight line by theoperator in a horizontal plane between a home position and a measurementtest position. The platform includes a mounting post normal to theplatform which is similar to the pivot bearing of the actuator. Theoperator mounts the head stack on the mounting post and rotates it to areferenced angular position where it is clamped.

The HSA is provided with a shipping comb which functions to maintain theadjacent head arms spaced apart a predetermined distance while the HSAis being tested before installation in the disk drive. The shipping combis arranged to pivot out of position during the gram load measuringoperation to permit each head to apply a force to a sensing device thatmeasures and displays the value of the gram load of that head to theoperator.

After positioning the HSA on the platform, the operator moves theplatform to the measurement position. As the heads reach the measurementposition, the shipping comb is pivoted out of position, allowing eachHGA arm of one pair to engage opposite sides of a rotatable camseparator pin. By rotating the pin 90 degrees, one head of the pair isallowed to engage its respective sensing device depending on thedirection of rotation. The heads are measured one at a time. Forexample, where the HSA includes four heads, four separate sensingdevices are provided so that the operator is advised if any head is outof specification.

With the decrease in size, the head arms become less sturdy and henceare more sensitive to the swaging operation with the result that thealignment of the heads may be adversely affected. Further, if one HGAarm proves, on testing of the head stack, to be out of specification forthe gram load, the possibility of manually adjusting the flexibleelement to obtain the correct biasing force is almost impossible.

The rework operation to replace the HGA having the incorrect gram loadwith a new head, or to at least salvage the good head arms, (usually 3arms) was very complicated due to the swaging construction and the morefragile nature of the smaller components. The present invention providesa method and apparatus which permits the selective adjustment of thegram load biasing force for each HGA in an HSA at a time in themanufacturing operation that the gram load for the HGAs of the HSA arebeing measured, thereby eliminating the need to rework a high percentageof HSAs where one head does not meet the specification for the correctgram load biasing force.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus topermit adjusting the gram load biasing force selectively for each HGA ofa Head Stack Assembly (HSA) which does not meet the established gramload specification involves the following functionalinter-relationships, embodied either as steps of a method or acombination of functionally inter-related hardware components, thepreferred embodiment of which is shown in the drawing and described inthe specification.

Since the measurement of the gram load on each HGA of the HSA iscurrently achieved by an operator and a measurement apparatus, thatapparatus has been modified to incorporate the necessary inter-relatedhardware that is the subject of the present invention. The movableplatform on which the HSA is mounted is employed in the preferredembodiment to position the HSA in an operable position relative to theGram Load Adjustment (GLA) station. The GLA station includes a verticalsupport tower which is provided with a plurality of horizontallyextending arm supports, each having a generally rectangularcross-section. The supports are vertically aligned and spaced apart adistance to permit each of the head arms to slide into one of the slotsdefined by adjacent supports as the support tower is moved sidewaystowards the HSA. The supports extend a distance from the verticalsupport tower structure sufficient to encompass the entire width of thehead arm. The function of the support tower and horizontal supports isto retain each HGA in a substantially rigid position in the event that aplus or minus adjustment is to be made to the gram load of the HGAflexible element to bring it into the range set forth in the HSAspecification.

The GLA station further includes a mechanism for applying an adjustingforce uniformly across the flexible element of the HGA at the pointwhere it joins the nut plate, in order to adjust the initial gram loadof the HGA to the correct load. The mechanism includes a pair of towerswhich are movable vertically and which support a pair of horizontallydisposed rigid pins. The vertical movement of the towers, up or down,moves both pins, one of which contacts the flexible element. Subsequentmovement adjusts the gram load by either increasing or decreasing thegram load initially built into the bend of the flexible element to bringit within acceptable limits.

The mechanism is arranged to permit the horizontally disposed rigid pinsto be selectively positioned vertically relative to the head stack inorder to select the HGA requiring the gram load adjustment. In thisregard, the rigid pins are attached to one tower in a cantileveredfashion and spaced apart vertically to permit the pins to straddle theflexible element of the selected head arm. The other tower is providedwith a pair of recesses that are adapted to receive the distal ends ofthe rigid pins as the first tower is moved horizontally and the pinsstraddle the flexible element.

The towers are movable vertically by a manually operated micrometer sothat the space between the pins can be positioned in the plane of theflexible member of any one of the HGAs. The adjustment in gram force ismade by the operator dialing a distance on the micrometer thatcorresponds to a the adjustment value. The micrometer moves the towersso that the rigid pins move in a vertical plane applying an equal forceacross the entire width of the flexible member. This prevents theflexible member from twisting about its lengthwise axis which wouldadversely affect the flying characteristics of the head.

Means are also provided to maintain the distal end of the arm containingthe magnetic head in substantially the same horizontal plane, when theadjusting force is applied to the flexible element.

It has been found that a linear relationship exists between the requiredforce adjustment and vertical movement of the pins as measured by themicrometer mechanism. For example, if the gram force of the head asoriginally measured is 0.01 gram less than the desired optimum force,the operator needs only to move the pins 0.001 millimeter. If howeverthe measurement is 0.02 grams less than desired, the operator would movethe pins vertically 0.002 millimeter.

The direction of vertical movement depends on whether the HGA is facingup or facing down, which in turn depends on the location of the head armin the head stack. If the HGA is facing down and the gram load needs tobe increased, the vertical movement is downward. If the gram load needsto be decreased the vertical movement is upward. If the HGA is facingupward, the above vertical direction for increasing the load would beupward and downward for decreasing the gram load.

An object of the present invention to provide an improved apparatus foradjusting the gram load of an HGA in a head stack assembly.

Another object of the present invention is to provide an improved methodof selectively adjusting the gram load of a selected HGA in a Head StackAssembly having a plurality of HGAs.

Another object is to provide an apparatus for adjusting the gram load ofan HGA to within a predetermined range in connection with the HSAmanufacturing step which measures the gram load of each HGA at the HSAlevel of assembly.

A further object of the present invention is to provide a method andapparatus which allows an operator to manually measure and adjust thegram load of each HGA of a HSA selectively in accordance withpredetermined specifications.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in greater detail with reference to thedrawing in which:

FIG. 1 is a schematic plan view of a typical disk drive;

FIG. 2 is an perspective view of a head stack assembly;

FIG. 3 is a side view of a head arm assembly;

FIG. 4 is a diagrammatic plan view of the apparatus embodying thepreferred embodiment of the present invention which illustrates thespatial relationships of the various major functions of the componentsof the novel apparatus of this invention;

FIG. 5 is a perspective view of the apparatus shown in FIG. 4 formeasuring and adjusting the gram load;

FIG. 6a is a schematic side view of the HGA shown in FIG. 3,illustrating how the HGA is held during an adjusting operation;

FIGS. 6b and 6c are schematic perspective views illustrating thefunction of the towers and rigid pins which apply the force to the HGAto adjust the gram load.

FIG. 7 is a flow chart of the steps involved in the method of thisinvention for adjusting the gram load of the head arm at the HSA level.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic plan view of a disk drive 10 which includes a baseplate 11 on which is mounted a plurality of magnetic disks 12 thatrotate about an axis 13 that is normal to the surface 14 of the baseplate 11. The disks 12 are rotated by means of a motor (not shown) at aconstant speed during the transfer of data to and from the disks 12 thatare positioned under the base plate 11. The disk surface 16 has arelatively large number of closely spaced concentric recording tracks17. The drive 10 includes a rotary type actuator 18 for positioningmagnetic heads 19 relative to the recording tracks 17 on the recordingsurfaces of disks 12. The magnetic heads 19 are rotated on pivot bearing18a and moved in an arc 20 across the surface of disk 12 during a trackaccessing operation.

FIG. 2 is an perspective view of the head stack assembly at themanufacturing level immediately prior to the step of measuring the gramload. As shown the HSA comprises an assembly of four HGAs designated 21athru 21d. Assemblies 21a and 21b have gram loads that bias the magneticheads towards each other. In operation the magnetic heads for HGAs 21aand 21b are biased toward and fly over opposite surfaces of the topmagnetic disk of a two disk stack. Heads for HGAs 21c and 21d aresimilarly arranged relative to the bottom disk of the two disk stack.

FIG. 3 is a side view of a single HGA 21. In general the functionalelements of the HGA 21 as shown in FIG. 3 comprises a relatively rigidsection 31 and a relatively flexible section 32, which are swagedtogether. The end of section 31 is provided with a circular openingwhich is adapted to receive the pivot bearing 18a that is part of theelectromagnetic actuator 18 which positions the heads in the disk drive10, as shown in FIG. 1.

An HGA comprising an air bearing slider 35 that supports a magnetictransducer, and a gimbal type mounting 36, is attached to the end 37 ofthe HGA 21. The bend 38 in the HGA 21, as shown, is in the area wherethe rigid section 31 ends and is obtained by bending the flexibleelement 32 to provide a predetermined gram load when the head is bentback to its initial horizontal position and when the HSA is positionedin the disk file 10. After the heads are assembled in the head stackassembly, a removable shipping comb is provided for the HSA that keepsthe heads separated during the subsequent manufacturing and testingoperations. The comb is removed when the HSA is installed in the diskdrive.

FIG. 4 is a diagrammatic plan view of the apparatus embodying thepreferred embodiment of the present invention which illustrates thespatial relationships of the various major functional components of theapparatus. The apparatus comprises a Gram Load Measuring station (GLM)41, a two section Gram Load Adjusting (GLA) station 42A and 42B, and anHSA delivery platform 43 that is movable manually by the operator from ahome position 44 to either an operable position in the GIM station 41 orthe GLA station 42.

The GLM station 41 is described with reference to FIG. 5 whichillustrates how the GLM and GLA stations have been combined. Any priorart gram load measuring apparatus may be employed in connection with thepresent invention to provide indications of the actual gram load on eachHGA in the stack. With reference to FIG. 5, the function of deliveringthe HSA to the measuring station is achieved by the delivery platform 43which is movable back and forth as indicated by bidirectional arrow 51from a home position as shown in FIG. 5. The HSA clamping platform 54 ismovable relative to platform 43 in a direction parallel to arrow 51, asindicated by bidirectional arrow 55. The HSA is moved to the measuringstation by the combined movements of platforms 43 and 54 being moved tothe left by the operator as seen in FIG. 5.

A comb remover device 56 functions to automatically remove a shippingcomb from the HSA when the HSA is moved toward the measuring station. Atower 60, which is movable bidirectionally in the directions of arrow53, contains a pair of pins 58 and 59 that slide between adjacent HGAs21 which are biased toward each other. The pins 58 and 59 are insertedbetween the head arms as the tower 57 is moved toward the HSA and beforethe shipping comb is automatically removed by device 56.

The gram load on each HGA is measured separately by rotating one of thepins 58 or 59 either clockwise or counterclockwise. Each pin 58 and 59has a semi-circular cross-section which allows the pin to function as aseparator cam when the circular portion of the pin engages the HGA.However when the cam is rotated 90 degrees, the separator function isremoved for one HGA so that the HGA is allowed to move toward the axisof the pin under the gram load built into the HGA. The magnetic head atthe end of the arm 21 that is allowed to move and engage one of foursurfaces 60a-60d provided on the tower 60. The gram load is thenrecorded and displayed to the operator. If the gram load is not withinspecified limits, the HSA is moved to the GLA station by the operatormoving the platform 43 to the right, as shown in FIG. 5. The gram loadmay be adjusted by the operator to meet the desired value at the GLAstations 42A and 42B.

The functional aspects of the Gram Load Adjust stations are described inconnection with FIGS. 6A-6C and the corresponding structural componentsshown in FIG. 5. The GLA 42A and 42B comprises a stationary towerdesignated with reference character 61 in FIG. 5, which is mounted onand movable with the main delivery platform 43. Tower 61 includes ablock 61a that is provided with three groups of cantilevered projectingelements which function to maintain each of the head arm assemblies in arelatively fixed position during the adjusting operation at the GLAstation.

The first group of cantilevered elements as shown in FIG. 6a comprisefour elements 62 which have rectangular cross-sections and are alignedvertically in a comb-type configuration. One element 62 is associatedwith each actuator arm 21 and is positioned, as shown in FIG. 6a, suchthat the rigid section 31 of the is maintained in a horizontal planewhen the shipping comb is removed and replaced with separators.

The second set of elements comprises a pair of separator pins 64 (seeFIG. 6A), which are associated with pairs of opposing HGAs 21. Pins 64function as separator pins by limiting the movement of the head in adirection caused by the initial gram loading force. The separator pins64 are aligned vertically and have a diameter dictated by the armspacing of the HSA. These pins function to prevent the heads of adjacenthead arms that are biased toward each other from coming in contact whenthe shipping comb is removed.

The third set of elements includes a pin 66 associated with the HGA 21,located on the opposite side of the HGA 21 from the separator pin 64 andoffset toward the distal end of the HGA as shown in FIG. 6a. Thefunction of the pin 66 is to restrain any vertical movement of the headend of the HGA that may result from an adjusting force being applied tothe HGA.

The adjusting station also includes a means for applying a bending forceto the flexible section of the head arm. FIGS. 6b and 6c illustrateschematically the function of adjusting the gram load by applying auniform force across the width of the flexible section at the pointwhere it joins the relatively rigid section of the HGA. As shown in FIG.6b, a tower post 70 is provided with a pair of vertically alignedhorizontally disposed cantilevered elements or pens 71. The post 70 ismovable in a direction indicated by arrow 72 parallel to the axes ofcantilevered elements 71. The post 70 is moved horizontally in thatdirection so that elements 71 straddle the flexible element 32 of HGA 21adjacent to the nut plate area 76.

A second post 73 is provided with a pair of recesses 74 for receivingthe distal ends of cantilevered elements 71 as shown in FIG. 6c. Theposts 70 and 73 are movable conjointly vertically as indicated bybidirectional arrow 75 in FIG. 6c. This movement which is controlled bythe operator permits the operator to position the pins 71 vertically sothat they are able to straddle a selected HGA. Subsequently, theoperator moves the pins 71 a predetermined distance to apply theappropriate force to correct the gram load. The pins 71 act as aforce-transmitting bar.

With reference to FIG. 5, the tower 61 comprises an inverted U-shapedmember which is mounted on and moves with main delivery platform 43. Thesupport block 61a, which supports the three groups of cantileveredelements 62, is slidably mounted on the inverted base of the U-shapedmember 61. The HSA is positioned in the adjust station 42A, 42B by theoperator and the support block 61a is moved in a direction towards theHSA until the respective cantilevered members are in position to performthe functions described earlier. The operator then removes the shippingcomb.

The mechanism to apply the adjusting force described functionally aboveand shown in FIGS. 6b and 6c comprises the horizontally movable tower 70and the tower 73 which is movable in a vertical direction conjointlywith tower 70. Tower 70 carries the pins 71 which straddle a selectedHGA and engage in the recesses 74 in the tower 73 as tower 70 is slidinto position.

The means for positioning the pins 71 vertically relative to the HGAs ofthe HSA comprises a micrometer 80, mounted to move the towers 70 and 73conjointly in a vertical direction independently of the horizontalmovement and position of tower 70. The micrometer 80 is provided with aknob 81 and a distance scale 82. The operator rotates knob 81 in adirection to move the towers 70 and 73 vertically while easing themovable tower horizontally towards the selected HGA needing adjustment.When correctly positioned vertically, tower 70 is slid into positionwith the pins 71 straddling the flexible section of the HGA and theirdistal ends engaged in the recesses 74 of tower 73.

The force required to adjust the gram load of the selected head towithin the required tolerances is obtained from a reference table thatconverts a required gram load adjustment to a vertical distance to movethe towers 70 and 73. The operator moves the towers 70 and 73 verticallyup or down the distance obtained from the table, as indicated on themillimeter micrometer scale 82, by rotating knob 81. The movement causesthe gram load to change accordingly in a substantially linear fashionover a wide range of gram load values.

In situations where the tolerance limits are quite small, such ashundredths of milligrams, it may be necessary to provide the operatorwith a more precise indication of when the pin 71 actually contacts theHGA, since some vertical tolerance must be provided in order for thepins to straddle the head arm. The actual point of contact can beprovided by any prior art sensing device which functions to provide anindication that two members are in contact. The sensing device wouldallow the operator to accurately measure the distance that themicrometer must move and hence obtain more consistent corrections.

FIG. 7 is a flow chart which illustrates the basic steps of the method.The flow chart is self-explanatory when read in connection with theabove detailed description of the HGA assembly. It should be understoodthat various modifications may be made within the scope of theinvention. For example, the measuring station need not be as describedsince the present invention may be employed separately from themeasuring station or in combination. Similarly, the path of the HSAmovable platform need not be in a straight line. The path is dependenton the relative positions of the GLM station and the GLA station.

What is claimed is:
 1. An apparatus for adjusting a gram load of aselected head gimbal assembly having a longitudinal axis while locatedin a head stack assembly having a plurality of head gimbal assemblies,each of said head gimbal assemblies includes an elongated flexiblemember having a predetermined bend that is transverse to thelongitudinal axis of said head gimbal assembly comprising:means forremovably mounting said head stack assembly for movement in a planeparallel to said longitudinal axis of said selected head gimbal assemblyto a gram load adjusting station; means for restraining movement of saidselected head gimbal assembly during a gram load adjustment; meanscomprising an elongated, rigid, straight bearing edge for applying aforce to said flexible member to adjust said gram load; means forpositioning said edge parallel to said bend, and in contact with thebend area of said flexible element; and means for moving said edge apredetermined distance for adjusting the gram load of said head gimbalassembly.
 2. The apparatus as in claim 1 including a gram load measuringstation for measuring the gram load of each said head gimbal assembliesin said head stack assembly, and wherein said means for removablymounting includes a slidable platform having a head stack assemblymounting post.
 3. The apparatus as in claim 2 in which said gram loadmeasuring station includes indicator means for providing an indicationto an operator that the gram load of said selected head gimbal assemblyneeds to be adjusted by a predetermined amount.
 4. An apparatus foradjusting a gram load of a selected head gimbal assembly having alongitudinal axis while located in a head stack assembly having aplurality of head gimbal assemblies, each of said head gimbal assembliesincludes an elongated flexible member having a predetermined bend thatis transverse to the longitudinal axis of said head gimbal assemblycomprising:means for removably mounting said head stack assembly formovement in a plane parallel to said longitudinal axis of said selectedhead gimbal assembly to a gram load adjusting station; means forrestraining movement of said selected head gimbal assembly during a gramload adjustment; means comprising an elongated, rigid, straight bearingedge for applying a force to said flexible member to adjust said gramload; means for positioning said edge parallel to said bend, and incontact with the bend area of said flexible element means for movingsaid edge a predetermined distance for adjusting the gram load of saidhead gimbal assemble; including a gram load measuring station formeasuring the gram load of each of said head gimbal assemblies in saidhead stack assembly, and wherein said means for removably mountingincludes a slidable platform having a head stack assembly mounting post;wherein said gram load measuring station includes indicator means forproviding an indication to an operator that the gram load of saidselected head gimbal assembly needs to be adjusted by a predeterminedamount; wherein said means for removably mounting includes means forsliding said platform in a plane along a path connecting respectiveoperating positions at said stations; and clamping means on saidmounting post for clamping said head stack assembly with said headgimbal assemblies substantially parallel to the plane of movement ofsaid platform and said longitudinal axis parallel to said path.
 5. Theapparatus as in claim 4 in which said means for restraining movement ofthe selected head gimbal assembly comprises a plurality of cantileveredelements disposed parallel to said plane, including a first set ofvertically aligned rigid elements, each having a rectangularcross-section and a length to permit each pair of adjacent elements torestrain movement of the selected head gimbal assembly when a force isapplied to said head gimbal assembly in a direction normal to saidplane.
 6. The apparatus as in claim 5 in which said plurality ofcantilevered elements includes a second set of vertically alignedseparator pins offset relative to said first set of elements andarranged to prevent the flexible members of adjacent head gimbalassemblies which are biased toward each other from coming in contact. 7.The apparatus as in claim 6 in which said means for restraining movementof the selected head gimbal assembly includes a block structure forsupporting said cantilevered elements, and means for reciprocally movingsaid structure parallel to said plane and normal to said path toposition said cantilevered elements into and out of a movementrestraining relationship with said head gimbal assemblies.
 8. Theapparatus as in claim 7 in which said means for positioning said edgeparallel to said bend and in contact with the bend area of said flexiblemember comprises:a first tower disposed normal to said plane formounting said edge in a cantilevered fashion; means for reciprocallymoving said first tower parallel to said plane and normal to said pathto position said edge across said bend; and a second tower adapted tosupport the distal end of said edge during the gram load adjustingoperation, said second tower disposed on the other side of said headstack assembly opposite said first tower and having a stationaryrelationship relative to said first tower to permit said distal end tobe supported.
 9. The apparatus as in claim 8 in which said means formoving said edge comprises a mechanism for conjointly moving said firstand second towers in a vertical direction relative to said plane topermit positioning said edge at a selected head gimbal assembly, priorto moving said first tower toward said head stack assembly to positionsaid edge in force-transmitting relationship with said bend of saidselected head gimbal assembly and the distal end of said edge in asupported relationship with said second tower.
 10. The apparatus as inclaim 9 in which said means for moving said edge comprises a micrometerfor moving said towers vertically a predetermined distance to cause thegram load of said head gimbal assembly provided by the bend in saidflexible member to be adjusted to a predetermined value, said micrometerhaving a distance scale for indicating to an operator when the verticaltravel corresponding to said predetermined value has been obtained. 11.An apparatus for adjusting a gram load of at least one head gimbalassembly having a longitudinal axis and while located in a head stackassembly having a plurality of head gimbal assemblies, each of said headgimbal assemblies includes an elongated flexible member having apredetermined bend that is transverse to the longitudinal axis of saidhead gimbal assembly, comprising:first means for removably mounting saidhead stack assembly for movement in a direction parallel to saidlongitudinal axis of said head gimbal assembly to a gram load adjustingstation, said first means comprising a platform and a mounting posthaving an axis disposed normal to said platform; means for maintainingthe head gimbal assemblies of said head stack assembly in a relativelyfixed position, including a support block having a plurality ofcantilevered support members positionable relative to said head gimbalassemblies for restraining movement of the head stack assembly during agram load adjustment, said support block being movable in a directionnormal to said longitudinal axis; a force-transmitting bar having anelongated bearing edge; means for positioning said bar with said edgedisposed transverse to the lengthwise axis of the selected head gimbalassembly at the point where the flexible element is bent, and inforce-transmitting contact with said flexible element; and means formoving said bar a predetermined distance for adjusting the gram load ofsaid head gimbal assembly that is provided by said flexible element.